The present invention relates to a disc drive storage system and, in particular, to a disc drive storage system having a head suspension assembly with a gram load reducer.
Disc drives of the "Winchester" type are well known in the industry. Such drives use rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers which write information to and read information from the disc surfaces.
An actuator mechanism moves the sliders from track to track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each head gimbal assembly. The suspension includes a load beam and a gimbal. The load beam provides a load force which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam, or is integrated in the load beam, to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
The slider includes an air bearing surface which faces the disc surface. As the disc rotates, the disc drags air under the slider and along the air bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the air bearing surface, air compression along the air flow path causes the air pressure between the disc and the air bearing surface to increase which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. This process is known as slider "take-off". A suction force may also be created between the disc and the air bearing surface, depending upon the geometry of the air bearing surface. The load force supplied by the load beam and the suction force counteract the hydrodynamic lifting force. The load force, the suction force and the hydrodynamic lifting force reach an equilibrium based upon the geometry of the slider and the speed of rotation of the disc. This equilibrium determines the flying height of the slider, and thus the resolution of the read and write transducer carried by the slider.
One of the major technical challenges for the design of head gimbal assemblies is to maintain a desirably low and flat flying height profile over the disc surface and to reduce mechanical interference between the head and disc. A low and flat fly height profile is achieved in part by providing the slider with an air bearing having a high stiffness. Unfortunately, this may lead to an undesired level of mechanical interference between the head and disc during take-off and landing. Also, the larger the load force, the higher the rotational velocity the disc must reach before the slider will lift and fly above the disc surface. A prolonged period of contact between the slider and the disc surface causes wear of the slider, the transducer and the disc surface.
Several attempts have been made to reduce mechanical interference between the head and disc, but these attempts have not reduced the interference dramatically. For example, a typical magnetic disc is coated with a thin layer of lubricant for reducing wear at the head and disc interface. However, when the disc stops rotating and the slider rests on the disc surface, the lubricant tends to pull the slider and the disc surface together by the action of meniscus surface tension. Since the stiction force must be overcome before the disc can move relative to the slider, the stiction force adversely affects contact start and stop (CSS) performance of the slider. This stiction force has been reduced slightly by texturing the take-off and landing zone of the disc surface. The preload force applied to the slider, however, remains one of the largest contributors to stiction.